Cow's milk allergy is nothing new. It has been around as long as humans have consumed the milk from cows. As early as 370 B.C., the Greek physician Hippocrates reported the case of a patient having an adverse reaction to cow's milk. Cow's milk is one of the most common food allergens, especially for children. Following relevant studies in Australia and Denmark, it has been estimated that around 2% of children will develop milk allergy during the first year of life. Whilst it may be a popular misconception that it is somehow "unnatural" to drink the milk of other animals, one would expect that the milk allergy rate of about 2% of infants to be much higher if it was truly "unnatural" to drink the milk of other animals.

While cow's milk allergy is primarily developed in infants under one year of age, it seems that many children, some three-quarters of those with milk allergy, can be expected to have grown out of this allergy by the time they reach three to four years of age. The total rate of milk allergies for adults in America is under 1%. One factor that must be taken into consideration when examining the reduced incidence of cow's milk allergy amongst adults, however, is the fact that adults generally have a greatly reduced milk intake compared to that of children.

Completely avoiding the associated protein allergens in milk for a few years appears to aid the process of outgrowing milk allergy. This is different from lactose intolerance, which tends to develop as people get older. The variance between milk allergy and milk intolerance occurs because milk allergy incorporates the immune system when reacting to milk protein as an allergen, while lactose intolerance does not. Although it rarely occurs, it is possible for a person to be both lactose intolerant and allergic to milk.

An allergy to cow's milk is actually based on an allergic reaction to the proteins commonly found in milk. Having become previously sensitised to these proteins, your immune system mistakenly interprets these proteins as a threat and releases chemicals to deal with the invader. One of these chemicals is histamine, which causes fluid leakage and dilates blood vessels. This results in swelling (angioedema), urticaria (hives), and itching. Because this reaction involves the immune system, it can engage multiple areas of the body in the response. At its most dangerous, this overreaction by the immune system can produce anaphylaxis, a life-threatening condition during which the blood pressure drops rapidly and the air passages swell to the extent that breathing becomes difficult. Fortunately, death or unconsciousness due to milk allergy is very rare.

Milk Proteins

The milk from cows contains about 30 protein components that can provoke an unwanted antibody response in humans. The actual process of digestion probably increases the number of possible antigens to over 100. It is the casein in milk that gives it its white appearance. This is the curd that forms when milk sours. Casein constitutes about 80% of the protein found in cow's milk. Skim milk is a product that is created when the casein is separated from whey in the milk. The whey, which consists of a multitude of other proteins, only constitutes around 20% of the protein in milk. Whey is the watery part of milk that is left when the curd is removed. It is still unclear which of all the proteins contained in milk is the most allergenic. Some people with milk allergy are only allergic to one of the two main proteins in milk, either casein or whey, whilst others are allergic to both.

Milk proteins remain mostly intact even when milk is converted into various types dairy products. Heat treatment, such as is used to create evaporated milk, only affects those proteins that are susceptible to heat, including some of the whey proteins. This is why, for example, someone who is only sensitive to the whey in milk may be able to ingest pasteurised milk. The casein proteins in milk are, however, the least susceptible to heat treatment. This means that someone who is allergic to the casein proteins in milk will probably be allergic to most types of milk and milk products.

Some people are so sensitive to milk protein that they can have an allergic reaction in response to very small amounts of it. For example, simply touching milk, kissing someone who has been drinking milk, or even accidentally inhaling particles of milk powder can trigger an allergic reaction.

Cow's Milk Allergy Symptoms

The reactions experienced by people with cow's milk allergy can be roughly divided into three basic categories. The first category encompasses the so-called "immediate" reaction that takes place within 45 minutes of consumption of milk. It is largely characterised by those symptoms relating to the skin. This category typically includes those who developed milk allergy as breastfeeding infants. The "immediate" category also encompasses those few people who are at risk of life-threatening anaphylaxis after coming into contact with milk allergens.

The symptoms for this group include rashes, itchy red skin or eyes, and urticaria (hives). Respiratory symptoms can include allergic rhinitis, coughing, wheezing, and possibly swelling (angioedema) of the airways, lips, face, tongue or throat. Those who experience this sort of early reaction are more likely to return a positive result during a skin prick allergy test. These IgE (Immunoglobulin E) mediated reactions will almost always return a positive result during RAST blood tests because of elevated IgE concentrations.

The second classification related to an "intermediate" level reaction. This is typically concentrated in the gut and takes place between 45 minutes to 20 hours after a moderate amount of milk protein is ingested. Gastrointestinal symptoms commonly include vomiting or diarrhoea. Only about a third of this group is likely to return a positive result in response to a skin prick test because these reactions are not usually IgE mediated.

A reaction 20 hours after a normal volume of milk is consumed is categorised as a "late" reaction. This will usually affect the skin, the gut, and possibly the respiratory tract. Typical symptoms include diarrhoea, vomiting, eczema, and asthmatic symptoms. Although only about one-fifth of people with this type of allergy will test positive during a skin prick test, most of them will return a positive reaction when an atopy patch test is applied to the skin of the back for the requisite 48 hours. These "late" reactions are rarely IgE mediated but are thought to involve white blood cells known as T-cells (T lymphocytes) instead.

Some people experience symptoms discomfort after drinking milk because of its texture and the perception that the mucus in the throat is thicker and harder to swallow. Fluids other than milk with a similar texture and consistency will also produce this feeling. It is not actually due to milk increasing the production of mucus, nor is it an allergy. This sensation can be avoided by reducing the intake of milk. Another complaint people sometimes have is that they find they start to cough after they drink cold milk. This is usually due to breathing in cool air as they drink the milk and should not occur if they let the milk warm a little before drinking it. Other possible adverse reactions to milk include gastroesophageal reflux disease (GORD), colitis, and eosinophilic oesophagitis.

Infants and Cow's Milk Allergy

Infants should not be fed cow's milk until they are older, regardless of whether the milk is in a low-fat or whole form. Otherwise it increases the chance that they will develop cow's milk allergy. Studies suggest that there is a higher incidence of cow's milk allergy among infants who are exposed to cow's milk early in their lives. The first three to four months of life represent the period when infants are most susceptible to this, especially if there is a family history of allergies. During the first few months of life, the small intestines have greater permeability to proteins. This means that this period of infancy sees small quantities of food being absorbed through the intestine. The rate of allergy sufferers appears to be reduced if cow's milk is not introduced until after a child is at least six months old, given that their gut has had a chance to "mature".

The chance of developing cow's milk allergy is increased if the family of the child has a history of atopic disease, as indicated by parents or siblings. Atopy is essentially a hereditary predisposition towards developing allergies. The incidence of allergies is approximately double the normal rates for families with a history of atopic disease. Eliminating the amount of highly allergenic food present in an infant's diet during the first six months of life can help reduce the incidence and severity of atopic diseases, including asthma and certain environmental allergies. While someone with milk allergy may also develop asthma, there is no casual relationship between the two conditions.

As well as protein, milk provides energy, fat, and calcium. Milk is also rich in nutrients, containing vitamins A, B12, and D, riboflavin, phosphorus and pantothenic acid. Breast milk remains the ideal food for infants and sometimes it is still tolerated by infants with cow's milk allergy simply because mother's milk does not contain the same proteins as cow's milk. If the symptoms exhibited by a totally breast fed infant do not improve, then the mother may need to restrict the amount of dairy products in her diet and take a calcium supplement instead. This is because cow's milk protein can be transferred to an infant via breast milk.

Mothers should not undertake a maternal diet restriction without appropriate medical and dietary advice. This is because eliminating milk may also reduce the intake of other important nutrients. Calcium, for example, is an important nutritional requirement and if milk and dairy products are eliminated from a diet then an alternative source of calcium is required. For adults, alternative sources of calcium include broccoli, figs, tofu, almonds, salmon with bones, and baked beans. It is worth noting that cow's milk allows for the superior absorption of calcium so a greater quantity of any alternative source of calcium is often required to achieve similar levels of nutrition. Calcium enriched rice milk and soy milk contain about the same amount of calcium as cow's milk and can help adults to reach daily calcium requirements. Soy, however, has its own allergenic profile.

An alternative to milk sometimes given to infants with cow's milk allergy, and who are over six months of age, is soy formula. Soy milk contains protein and fat and some types are calcium enriched. Be aware that it may not be suitable as the basis for an elimination diet because some children with cow's milk allergy will also have an adverse reaction to soy, as it is also a common allergen. Some estimates suggest that around 30% of infants with milk allergy will have concomitant soy milk allergy. Some medical practitioners are reluctant to recommend soy as an alternative to cow's milk because of the perceived risk of children also having adverse reactions to soy. Infants with cow's milk allergy are often more likely to develop allergies to other foods so care should be taken in introducing new foods into their diet during this early stage.

Adults sometimes use rice milk because it is unlikely to trigger an allergic response or further sensitise an allergic individual. Yet because it is a substance with a low fat and protein content, rice milk may not be a suitable nutritional substitute for other types of milk, even when fortified with calcium. Other types of milk, like oat milk, almond milk, or sesame milk, have low nutrient and calcium content and are not recommended for children because they are a potential allergy risk.

The milk of other animals is usually not an acceptable alternative. Goat's milk is no less allergenic to someone with milk allergy than cow's milk and shares essentially the same protein structure. Goat's milk has a degree of cross-reactivity with cow's milk so it is often not tolerated by children who are allergic to cow's milk. Goat's milk is also a poor substitute for cow's milk because, although it is rich in minerals, it lacks certain vitamins needed to be nutritionally complete. Sheep's milk also appears to have a great deal of antigenic similarity with the beta-lactoglobulin in the whey component of cow milk. The similarity between goat, sheep and cow's milk makes the other two varieties of milk unsuitable alternatives for someone who has an allergy to cow's milk. If a child has a propensity to develop other allergies then using the milk of another animal may only serve to sensitise them to that as well.

Some standard infant formulas cannot be used by babies with milk allergies because they still include reduced concentrations of cow's milk proteins. Hypoallergenic infant formulas can be a way of providing an alternative source of the nutrients necessary to maintain a healthy and balanced diet. Popular amongst these, despite being expensive and having something of a bitter taste, is extensively hydrolysed formulae (EHF). Note that EHF is different from the partially hydrolysed variety that is also available. It is created by a process known as enzymatic hydrolysis. Casein hydrolysates have been used for a number decades and, although whey hydrolysates are a newer alternative, both feature a similar level of clinical tolerance. The denaturation of the whey components of the milk leaves the casein intact but does enable some children to tolerate cow's milk, namely those who are allergic to the whey proteins. Even hypoallergenic formulas are not non-allergenic and a small proportion of children may still react to them, depending on the formula. An amino acid based formula is used in the around 10% of cases where children with milk allergies are also allergic to EHF or do not respond to an EHF-based elimination diet.

The term "multiple food protein allergy" (MFPA) is used to describe an allergy that contains more than one basic food, such as milk, wheat, and egg. An allergy to cow's milk can occur in association with other food allergies and should be investigated if an infant is not responding to an extensively hydrolysed formula (EHF) based diet. If a child has MFPA then a doctor may recommend that they continue to use a hypoallergenic formula until up to two years of age.

Identifying Cow's Milk Allergens

Milk can be found in a wide variety of products, some of which are more obvious than others. Foods that may contain milk protein are too numerous to list but include bread, cereals, baked goods, batter-fried food, soups, sauces, puddings, cheeses, sweets, and ice cream. It is not just food products that contain milk. Some medicines and cosmetics include milk protein or lactose in their ingredients.

There are many ingredients in products that contain milk but may be listed under a different name. The obvious ones are milk, pasteurised milk, dried milk, full cream milk powder, and skim milk powder. Extracted milk proteins may also be added to foods where they will retain their antigenicity. These proteins may be described as casein, caseinate, whey or whey powder. Other ingredients that contain milk protein include dry milk solids, milk derivate, butterfat, lactalbumin, sour cream, yoghurt, cream curds, artificial butter flavour or high protein flavour. Milk may be used in emulsions and may be described as emulsifier or even just "protein" on the label. Be aware that milk may have been used to make some of the ingredients used in the product, like margarine or bread crumbs, but the presence of milk in them is not listed.

Milk, dairy products, and foods containing milk-based ingredients need to be avoided if you are allergic to them. It is a myth that periodic exposure to milk will help to build tolerance to the allergen because this does more harm than good. The more you can totally avoid the allergen, the better your chances are of outgrowing the allergy. The safest course of action is to avoid all dairy products.

Avoiding dairy products is not always easy for children. Parents should check the ingredients of products and avoid any that list cow or goat's milk, butter, cheese, butter milk cream, ghee, margarine containing milk, cream fraiche, milk powder, casein or whey as ingredients. The task is complicated by the fact that sometimes a particular brand of margarine will actually have two variants, one that contains dairy and one that is dairy-free. The "full fat" and the "light" version of the same product may also constitute different dairy and dairy-free ingredients. The FDA in America allows foods containing casein to be labelled "non-dairy", which is clearly not the same a "dairy-free". Many Kosher foods are labelled as "Pareve" or "Parve", which are Kosher terms indicating that these products do not contain any milk or meat. If you are unsure about the ingredients of a product you should contact the manufacturer or local distributor for information on the exact contents of the product.

Often organisations within a particular country can assist the consumer by producing a commercial food list that helps to define foods that are safe to eat. In New Zealand, for example, the New Zealand Therapeutic Database compiles such a list. This lists the brand name foods available on the New Zealand market and helps define those products that contain milk or are considered lactose free.

Milk contamination is possible if the same machinery is used to manufacture a variety of products. The product may contain a warning to the effect that the product "may contain traces of dairy" and for some people a trace of milk protein is all that is required to provoke a reaction. Keep in mind that manufacturers can change their ingredients at any time so you need to constantly check ingredient listings.

Care should be taken if an establishment uses utensils to serve food that may have previously come into contact with milk protein.

Lactose Intolerance

Milk lies at the centre of both milk allergy and lactose intolerance but they are separate conditions with different causes. Lactose intolerance results from a deficiency in the enzyme lactase, the enzyme that helps the body to digest the milk sugar lactose. Lactose, a disaccharide, is composed of two simple sugars, or monosaccharides, and lactase breaks it down so that the intestine can absorb and digest it. Lactose is found in all kinds of milk, including cow, goat, and sheep's milk. Without sufficient lactase, the lactose is broken down by bacterial fermentation instead. It is this fermentation process that releases the acids, carbon dioxide and hydrogen gas that produce the symptoms of lactose intolerance.

Although the actual incidence of lactose intolerance is affected by a person's age and racial background, it is estimated that over half of the world's adult population has a degree of lactose intolerance. While the estimates for lactose intolerance amongst Caucasians is around 15%, the percentage for African Americans, Native Americans, Hispanics and Asians is much higher. Lactose intolerance is different from an allergy because it is actually rare in the first two years of life, while milk allergy usually develops in the first six months of life.

The symptoms of lactose intolerance generally appear within several hours of lactose being ingested, although it is not uncommon for some milk and milk-based products to be tolerated without manifesting the usual symptoms. Some of them are similar to those of milk allergy, including vomiting, watery diarrhoea, and abdominal pain. Lactose intolerance, however, does not involve the body's immune system as an allergy does but is focused on the GI tract. These symptoms are mostly located in the lower intestines. Lactose intolerance sufferers may also experience gas, flatulence, cramps and a sensation of feeling bloated. Although it may cause discomfort, this condition in not dangerous and cannot trigger anaphylactic shock.

These symptoms are dose related, which means that some people with the condition can have small amounts of lactose with little or no effect. The level of lactose malabsorption also creates variance in the amount of lactose tolerated.

The treatment for lactose intolerance involves avoiding those dairy products that contain lactose. Some dairy foods only contain a small amount of lactose. Fermented milk products such as yoghurt and sour cream only contain low levels of lactose because much of it has been converted into lactic acid. Other dairy products low in lactose include aged cheese such as cheddar, Swiss, camembert, parmesan and goat's cheese. On the other hand, goat's milk and sheep's milk are not low in lactose and are not suitable for use in a reduced lactose diet.

Lactose intolerance is not an issue when consuming yoghurt, for example, but yoghurt presents a problem for milk allergy sufferers because the milk proteins remain. People with milk allergy should not expect to eat products that are listed as "lactose-free" and not suffer from the symptoms of their allergy. Unlike milk allergy, where the milk protein is the problem, changing the amount of milk sugar used in the product can help lactose intolerance.

Some people take the lactase enzyme in tablet, capsule or powder form before consuming a meal that contains lactose, to assist with its digestion. Some health stores carry lactose-reduced, low-fat milk, which is produced especially for those with lactose intolerance.

Your doctor or a registered dietician can help you to outline a low lactose diet or tell you whether you simply need to reduce your dairy food intake. One possible test related to lactose intolerance is a breath hydrogen excretion test, which may be applied after lactose has been administered to a patient.

Diagnosis of Cow's Milk Allergy

Skin prick tests or RAST (Radioallergosorbent) blood tests are most useful in identifying those with "immediate" milk allergies because they are usually IgE mediated. The skin prick test (SPT) and ImmunoCAP/RAST test measure IgE antibodies for specific whole milk proteins. They are often less useful in those instances where milk allergy causes "intermediate" or "late" reactions and the milk proteins are no longer intact. Digested fractions of each of the milk proteins may induce the production of different types of antibodies, including Immunoglobulin E, A, and G, triggering complex immune system responses.

Another complication is that milk antigens tend to get through the GIT (gastrointestinal tract) mucosa intact so they are often responsible for a range of delayed immune responses. These reactions do not depend on IgE and so will not show up during standard skin tests. It is important that a doctor or allergist is given as complete history of symptoms to help them with their diagnosis.

If both the skin and blood tests are negative for allergies then a double-blind placebo-controlled food challenge (DBPCFC) can be used as a test method that eliminates both patient and administrator bias. This challenge involves gradually feeding increasing doses of food suspected of causing a reaction at predetermined time intervals to see whether it is tolerated or whether it results in allergy symptoms, all under controlled conditions. A double-blind placebo-controlled food challenge will not be undertaken if there is a family history of anaphylaxis.

An elimination diet may be used to test for an allergy to cow's milk. The elimination diet involves the removal of all dairy products and foods from a person's diet for a period of one to two weeks. A diary is kept recording all food consumed and any symptoms that result. Milk and dairy products are then slowly reintroduced into the diet under the supervision of a doctor or an allergist, with special care being taken if your family has a history of atopic disease.

The treatment of cow's milk allergy usually involves removing cow's milk products from the diet and their substitution with an alternative source of the required nutrients.